BRAKE UNIT, BRAKE ACTUATOR AND METHOD TO MANUFACTURE A BRAKE ACTUATOR
FIELD OF THE INVENTION This invention relates to a brake unit, a brake actuator and a method for manufacturing a brake actuator.
BACKGROUND OF THE INVENTION Motor vehicles are equipped with various types of brakes. For example, heavy vehicles are usually equipped with air brakes. The actuator of air brakes generally includes a housing defining an air chamber, a movable piston located in the housing and a push rod connected to the piston. The push rod extends outside the housing and the end of the push rod that is outside the housing is connected with a yoke. In the U.S. patent UU No. 6,253,890 an example is described. The yoke is connected to a cam by means of an articulated connection. When compressed air is supplied to the air chamber, the piston / push rod / yoke unit extends from the chamber, rotates the cam and pushes the brake shoes into contact with the brake drum. When the compressed air is exhausted from the chamber, the piston / pushrod / yoke unit retracts into the air chamber and the cam rotates in the reverse direction, so that the brake shoes are released from the brake drum. Ideally, when the brakes are released, that is, they stop being applied, there is an optimum gap between the brake shoes and the brake drum. This separation must be uniform in all the brakes, so that the wheels apply uniform braking forces on both sides of the vehicle. The separation must also be small, so that the piston / push rod / yoke unit extending from the air chamber needs to travel only a small distance to engage with the brakes. However, the clearance must be sufficient to prevent the brake shoes from dragging on the drum, even when hot and expanded by temperature. To adjust the gap between the brake shoes and the brake drum when the brakes are not being applied an automatic slack adjuster is used. A typical automatic slack adjuster includes a worm gear that is wedged or connected by keys to the arrow on the cam that moves the brake shoes. A helical transmission shaft, mounted to rotate about an axis perpendicular to the axis of the cam, engages with the worm gear to establish the angular position between the housing of the clearance adjuster and the arrow of the cam. A device is provided for rotating the worm gear and automatically changing the angular position between the seat of the slack adjuster and the arrow of the cam to eliminate the slack as the brake shoe becomes worn. The device includes a toothed conical clutch that can be used to disengage the adjustment mechanism during the portion of the elasticity of the brake application, to obtain the function of adjusting the clearance. During the adjustment, which is usually performed at the time of releasing the brakes, the clutch engages and transmits an angular movement and a torque to perform the adjustment of the clearance. In the U.S. patent UU No. 5,350,043 describes a typical automatic slack adjuster, the disclosure of which is incorporated herein by reference herein. In order for the automatic slack adjuster to work properly, the push rod must be within a certain range of length. In various vehicle configurations, different lengths of push rods are used to ensure proper operation of the automatic slack adjuster. The yoke is then permanently connected to one end of the push rod. In general, the yoke is permanently attached to the push rod by means of welding. However, the yoke soldier on the push rod has several disadvantages. For example, welding equipment is relatively expensive. And the heat generated by the welding can weaken the yoke or the push rod.
SUMMARY OF THE INVENTION In accordance with one aspect of the invention, a brake unit includes a brake, an actuator and an automatic slack adjuster to adjust the spacing between the brake shoes and the brake drum. The actuator includes a housing, a movable piston located in the housing, a yoke located outside the housing and a push rod that extends through the housing. The push rod is connected to the piston and an end portion of the push rod forms a rivet that connects the yoke to the push rod. In accordance with another aspect of the invention, a brake actuator includes a housing, a movable piston located in the housing, a yoke located outside the housing and a push rod extending through the housing. The push rod is connected to the piston and an end portion of the push rod forms a rivet that connects the yoke to the push rod. Preferably, the yoke includes a through hole and the push rod extends through the through hole of the yoke. The end of the push rod may be radially larger than the through hole to prevent the yoke from slipping off the end portion of the push rod. The end portion of the push rod may include a notch. In a preferred embodiment, the end portion of the push rod is radially smaller than the rest of the push rod. For example, the end portion of the push rod may have a first diameter and the rest of the push rod has a second diameter that is greater than the first diameter. The through hole may be radially larger than the end portion of the push rod, although it may be radially smaller than the rest of the push rod. For example, the through hole may have a third diameter that is larger than the first diameter, but that is smaller than the second diameter. As a result, the yoke can be mounted on the end portion of the push rod, but can not be mounted on the rest of the push rod. When the yoke is mounted on the end portion of the push rod, it can rest against one end of the rest of the push rod, the end of which forms the interface between the end portion of the push rod and the rest of the rod. of push. In accordance with a further aspect of the invention, a method for manufacturing a brake actuator includes extending an end portion of a push rod of the brake actuator through a through hole of a yoke of the brake actuator and radially extending the end of the push rod to a size that is radially greater than the through-hole to prevent the yoke from slipping off the end portion of the push rod. The method may further include creating a notch in the end portion of the push rod. The present invention has several advantages. For example, when compared to welding equipment, riveting equipment is less expensive. Additionally, the riveting does not weaken the yoke or the push rod. Other objects, advantages and novel features of the present invention will be apparent from the following detailed description of the invention when taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a brake actuator in accordance with one embodiment of the present invention. Figure 2 is a partial cross-sectional view of a rivet connection between the push rod and the yoke of the brake actuator shown in Figure 1. Figures 3a and 3b are partial cross-sectional views of the before and after, which illustrate the assembly of the rivet connection between the push rod and the yoke of the brake actuator shown in Figure 1.
DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates a preferred brake actuator (10) of the present invention. The rest of the brake unit is not specifically illustrated here, because in the US patents UU Nos. 5,350,043 and 6,253,890 are described and examples are shown, both documents are incorporated by reference herein. The brake actuator (10) includes a housing (12), a movable pi (14) located in the housing (12), a yoke (16) located outside the housing (12) and a push rod (18) that is extends through accommodation (12). The push rod (18) is connected to the pi (14) and an end portion (20) of the push rod (18) forms a rivet (22) that joins the yoke (16) with the push rod ( 18). The housing (12) can have any suitable configuration, although it usually has a generally hollow cylindrical configuration. The pi (14), normally configured as a cylinder or a disk plate, can be placed in the housing (12), so that it can move in the housing (12) in the axial direction. A seal (24) is preferably placed between the housing (12) and the pi (14). The seal can be a seal ring or a seal membrane. The push rod (18) has a generally elongated configuration. The cross section of the push rod (18) can have any suitable shape, such as circular, triangular or square. The yoke (16) has the general configuration of a fork, although it can be configured in any way that allows it to connect the pi-push rod unit to the rest of the brake unit. As illustrated in Figure 2, the yoke (16) preferably includes a through hole (26) and the push rod (18) extends through the through hole (26) of the yoke (16) to connect the yoke (16). push rod (18) with the yoke (16). The end portion (20) of the push rod (18) can be radially larger than the through hole (26) to form the rivet (22), which prevents the yoke (16) from slipping out of the portion. of end (20) of the push rod (18). The end portion (20) of the push rod (18) can include a recess (28). The notch (28) facilitates the deforming of the end portion (20) of the push rod (18) to make it radially larger than the through hole (26) and form the rivet (22). In a preferred embodiment, the end portion (20) of the push rod (18) is radially smaller than the rest of the push rod (18). For example, the end portion (20) of the push rod (18) can have a first diameter and the rest of the push rod (18) has a second diameter that is larger than the first diameter. The through hole (26) may be radially larger than the end portion (20) of the push rod (18), although it may be radially smaller than the rest of the push rod (18). For example, the through hole (26) may have a third diameter that is larger than the first diameter, but that is smaller than the second diameter. As a result, the yoke (16) can be mounted on the end portion (20) of the push rod (18), but can not be mounted on the rest of the push rod (18). When the yoke is mounted on the end portion (20) of the push rod (18), it can rest against one end (30) of the rest of the push rod (18), whose end (30) forms the interface between the end portion (20) of the push rod (18) and the rest of the push rod (18). In accordance with a further aspect of the invention, a method for manufacturing a brake actuator includes first extending an end portion (20) of a push rod (18) of the brake actuator through the through hole (26) of a brake actuator (18). yoke (16) of the brake actuator, as shown in Figure 3a (this figure does not include the notch (28) shown in Figure 2). Once the end portion (20) is fully seated in the hole (26), the end portion (20) is radially expanded to a size that is radially greater than the through hole (26) to prevent the yoke ( 16) slide out of the end portion (20) of the push rod (18), as shown in Figure 3b. This expansion can be generated by pressing, for example, a flare tool (32) on the exposed end of the end portion (20) to form the yoke retention rivet (22) shown in Figure 3b. Preferably, the tool is pressed into the end portion (22) using an impact technique, since the traditional processes that form the rivet, such as, for example, the riveting riveting can not be used by the close proximity of the branches from the fork of the yoke. Because the brake application forces, which are normally of the order of (200-400 pounds), are transported by the end (30) and the return forces of the brake actuator are much lower (usually in the order of ( 60 lbs)), the push-yoke link thus formed is sufficient to withstand the typical service interval of the brake actuation forces. The foregoing description has been set forth only to illustrate the invention and is not intended to limit it. Since modifications to the described embodiments embodying the spirit and substance of the invention may occur to those skilled in the art, it should be understood that the invention includes everything within the scope of the appended claims and their equivalents.